Noise muffler having a unique pressure safety valve

ABSTRACT

A muffler for reducing the noise level of a noise carrying gaseous flow having a fiberglass depth type filter and a pleated paper filter mounted within a metallic canister. The depth type filter has a sufficient thickness and density to break up an acoustic wave and thereby reduce the noise level accompanying a gas flow through the filter to a predetermined level. A groove is formed in one solid portion of the metallic housing. Gas flow introduced into the housing can reach this housing portion without passing through the filter. The groove weakens this portion of the housing so that it will rupture along the groove in response to too great a gaseous pressure. The groove has a half-circle shape so that the housing portions on opposite sides of the groove will only be bent during rupture. No part of the housing will be broken off during rupture and become a dangerous projectile.

United States Patent [151 3,680,659 Kasten 1 Aug. 1, 1972 [54] NOISEMUFFLER HAVING A FOREIGN PATENTS 0R APPLICATIONS PRESSURE SAFETY VALVE[72] Inventor: Walter Kasten, Franklin, Mich. [73] Assignee: The BendixCorporation [22] Filed: Aug. 23, 1971 [21] Appl. No.: 173,756

[52] U.S. C1 ..l81/36 A, 181/37, 181/55, 181/60 [51] Int. Cl. ..F0lnl/l0, FOln 3/02, FOln 7/00 [58] Field of Search ..181/35 R, 35 A, 36 R,36 A, 181/37, 42, 50, 60; 55/276 [56] References Cited UNITED STATESPATENTS 291,762 l/1884 Nason ..181/60 2,222,703 11/1940 Bixler l 8 l/372,600,236 6/ 1952 Gibel ..181/60 2,815,088 12/1957 Gibel ..181/36 A3,293,830 12/1966 McKinley ..181/35 A 3,339,668 9/1967 Trainor ..18l/373,380,553 4/1968 Gibel ..l81/60 3,561,561 2/1971 Trainor ..l81/551,269,772 7/1961 France ..l8l/60 Primary Examiner-Robert S. Ward, Jr.Attorney-John S. Bell [57] ABSTRACT A mufller for reducing the noiselevel of a noise carrying gaseous flow having a fiberglass depth typefilter and a pleated paper filter mounted within a metallic canister.The depth type filter has a sufficient thickness and density to break upan acoustic wave sides of the groove will only be bent during rupture.

No part of the housing will be broken off during rupture and become adangerous projectile.

3 Claims, 3 Drawing Figures NOISE MUFFLER HAVING A UNIQUE PRESSURESAFETY VALVE FIELD OF THE INVENTION Noise mufllers.

BACKGROUND OF THE INVENTION Compressed air is used in many machines andother manufacturing applications. For example, it is used to drive aircompressors and air-hammers, to open and close molds infoundrys, toactivate clamping fixtures, to operate piston pumps, and for any numberof other applications. Exhaust air is discharged from these and similarmachines at high velocities so that the discharge generates objectionalnoise that can cause ear damage as well as operator fatigue. Inrecognition of the harmful effects of high noise levels Federal noiselevel exposure standards have been developed by the Department of Laborand incorporated into the health and safety regulations of theWalsh-Healey Act. These standards require that an operator not beexposed to particular average noise levels for more than certain statedtimes. For example, an operator cannot be exposed to an average noiselevel of 95 decibels for more than four hours a day, and cannot beexposed to an average noise level of 105 decibels for more than 1 hourin a day. Many industrial machines operate at an unacceptably high noiselevel. For example, air hammers and vacuum pumps operate at noise levelsof 107 and 108 decibels, respectively. An air hammer on a steel tankoperates at an average noise level of I21 decibels. By comparison, a jetairliner flying only 500 feet overhead creates only a l decibel averagenoise level.

In addition to the undesirable high noise level of industrial machinesutilizing compressed air, lubricating oil in liquid or mist form isusually added to the air supplied to those machines in order to preventscruffing or sizing of the moving parts. This oil is emitted with theexhaust air in the form of a highly dispersed mist. This oil mist notonly coats lighting fixtures, windows, safety glasses, and othermaterial to cause a high maintenance expense, but also may cause certainrespiratory diseases.

SUMMARY OF THE INVENTION This invention comprises a low-cost noisemufiler that can be attached to an outlet or exhaust port of an airoperated machine, and that will reduce the noise level of the exhaustdischarge to an acceptable low level. The noise filter of this inventionalso removes contaminants from the noise carrying air discharge.

The subject invention includes a porous material having sufficientthickness and density to break up an acoustic wave and reduce the noiselevel of a gaseous discharge to a predetermined low level. The porousmaterial is mounted in a housing having a perforated portion providingan outlet flow path from the muffler and a solid portion impervious togaseous flow. The porous material is mounted in substantially air tightcontact with the solid portion of the housing so that all gaseous flowreceived by the muffler must pass through the porous material to reachthe perforated housing portion and be expelled from the muffler.

A groove is formed on one area of the solid portion of the housing. Gasflow introduced into the housing can reach this solid portion withoutpassing through the porous material. This groove weakens the housing sothat it will rupture along the groove in response to too great apressure. The groove does not define a closed path, but instead has abeginning and an end displaced a sufficient distance from the beginningso that the housing portions on opposite sides of the groove will bebent during rupture. But, no part of the housing will be broken offduring a rupture and become a dangerous projectile. This groove formedin a solid portion of the housing of the muffler thus comprises a safetypressure valve that is substantially safer than a valve such as apop-off rubber disc or plug that is broken completely free from thehousing and becomes a dangerous projectile when pressure within thehousing reaches a predetermined level. The groove safety valve of thisinvention is substantially cheaper and easier to construct than is aspring operated pressure relief valve.

The porous noise reducing material, which comprises a fiberglass depthtype filter in the embodiment illustrated herein, also coalesces vaporcontaminants, such as oil vapors in the gaseous flow, and removes thosevapors from the flow. In the embodiment illustrated herein, a pleatedpaper filter is disposed upstream from the depth type filter to removesolid particle contaminants from the flow. The removed contaminants areheld by the pleated paper and the depth type filters. These contaminantsreduce the porosity of the filters to air flow. When they become cloggedso that pressure reaches a predetermined level within the muffler, thegroove safety valve ruptures indicating that the mufiler needs to bereplaced.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features, andadvantages of this invention, which is defined by the appended claims,will become apparent from a consideration of the following descriptionand the accompanying drawings in which:

FIG. 1 is a schematic, cut-away, two-dimensional plan view of oneembodiment of the noise mufiler of this invention;

FIG. 2 is a two-dimensional, plan view of the noise muffler of FIG. 1cut-away and illustrated along line 2-2; and

FIG. 3 is a cut-away two-dimensional view from the position defined byline 33 of the portion of the housing of the muffler of FIGS. 1 and 2having a rupture groove formed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates anoise muffler 10 comprising a metallic canister housing 12 having solidend plates 14 and 16 which are impervious to gas fiow. Housing 12 alsoincludes a cylindrical side wall 18 having perforations 20 which formoutlet ports for air flow from the muffler 10. A hollow fitting 22 isattached to the end wall 16. Fitting 22 is adapted to be attached to anair outlet or exhaust port of a machine to provide a substantiallyairtight or leakproof flow line from the machine exhaust port to theinside of muffler 10. A cylinder 24 of material that is porous to airflow, namely, a fiberglass bat or filter, is disposed inside housing 12.The fiberglass material forming cylinder 24 has a sufficient thicknessand density to break up an acoustic wave and reduce the noise levelaccompanying gaseous flow introduced into muffler to a predetermined,acceptable low level. The opposite ends of cylinder 24 are glued to thesolid end caps 14 and 16 around the entire circumference of the cylinderso that substantially all air introduced into the muffler 10 must passthrough the porous fiberglass material. A cylindrical pleated paperfilter 26 forremoving solid particles is disposed inside of, orin otherwords upstream from, the porous fiberglass cylinder 24. I

As is seen in FIGS. 2 and 3, as well as FIG. 1, noise muffler 10includes a groove 28 formed in depressed portion 30 of solid end cap 14.Depressed portion 30 fits inside of pleated paper filter 26, and airintroduced into muffler 10 can reach that portion without passingthrough any filter element. Groove 28 weakens portion 30 of end cap 13so that it ruptures along groove 28 in response to too great a pressurebeing developed inside muffler l0. Groove 28 does not define a completeclosed path, but instead is a semi-circle having opposite ends displacedfrom each other a sufficient distance so that the portions of end caps14 on opposite sides of groove 28 will merely be bent with respect toeach other during a rupture. That is, the portion of end cap 14partially encircled by groove 28 is merely bent to occupy positions 32shown in FIG. 1 during a rupture. No part of the housing 12 will bebroken off and propelled to become a dangerous projectile.

The precise dimensions for any particular embodiment of noise muffler 10may be determined experimentally. Porous cylinder 24 must have a densitysufficient to reduce the noise level of a gaseous flow to an acceptablevalue. A more dense material provides a greater noise reduction thandoes a less dense material. However, cylinder 24 cannot present toogreat an obstruction to air flow or it will slow the operation of themachine to which it is attached. That is, air is exhausted fromcompressors and similar machines in order to enable a particular part tobe moved during operation. The rate at which air is exhausted from themachine determines the rate at which the machine operates. Theobstruction to air flow provided by a muffler, such as muffler 10, isdecreased as the density of cylinder 24 is decreased. And, theobstruction of such a muffler is decreased'as the cross-sectional innersurface area of cylinder 24 is increased. In addition, the groove 28must be formedto a depth such that the filter will rupture at a pressureapproximately equal to a predetermined pressure.

One embodiment that has been found useful for many applicationscomprises a cylindrical muffler similar to that shown having a length ofabout 8 inches. The porous material 24 is formed from a fiberglass bathaving a density of about 0.045 lbs/cu. ft., having a thickness of aboutone-half inch, and having an inner diameter of about 2% inches. In thisembodiment, the housing 12 is formed from 0.025 stock steel plate, andgroove 28 is cut to a depth of 0.020 inches. A rupture occurs at apressure between 40 and 60 lbs./sq. in.

In operation, fitting 22 is attached to a gaseous exhaust port and a gasflow is introduced into the muffler 10. This gas flow passes throughporous filters 24 and 26 which break up the acoustic wave traveling withthat gas flow and reduce the noise level associated with that flow.Filter 26 removes solid particle contaminants are held by those filtersso thatthe filters ultimately become clogged. The clogging of filters 24and 26 causes the pressure within muffler 10 to increase. Muffler 10 isdesigned so that a rupture occurs along groove 28 when filters 24 and 26are substantially completely clogged. After a rupture has occurred, theloud sound of gaseous flow escaping through the rupture will indicate toan operator that a replacement is required if he has not actuallywitnessed the rupture or if he is not in a position to view the bentportion of end cap 14. The 8-inch muffler embodiment described abovepresents a relatively small obstruction or restriction to air flow. Theair flow obstruction of a muffler is determined by measuring thepressure drop across that muffler. An air flow of 100 cubic feet perminute undergoes a pressure drop of about 2 lbs/sq. in., and an airflow'of 150 cu. ft./min. undergoes a pressure drop of 4lbs./sq. in. Theamount of noise reduction is dependent upon the frequency of the noiseor sound source accompanying the gas flow. A to decibel noise level inthe 1,000 cycle per second frequency range, which is the range to whichthe human ear is most sensitive, is reduced by the above described8-inch muffler to approximately 60 decibels. A 95 to 100 decibel noiselevel in the 2,000 cycle per second frequency range is reduced toapproximately 65 decibels. A 90 decibel noise level in the 500 cycle persecond frequency range is reduced to slightly below 60 decibels. A 60decibel noise level is a relatively low and clearly acceptable level. Itis the level of ordinary conversation. The muffler of this invention is,therefore, an inexpensive and simple device that reduces the noise levelof very loud and irritating noises to a completely acceptable level.

Having thus described one embodiment of the invention, a number ofmodifications will readily occur to those skilled in the art. Therefore,what is claimed is:

l. A noise muffler for reducing the noise level of a noise carryinggaseous discharge from a port, and having a unique safety valvecomprising:

a housing having a perforated portion providing an outlet path from saidhousing for gaseous flow and a solid portion impervious to gaseous flow;

fitting means adapted to be attached to said port to provide asubstantially airtight path between said port and the inside of saidhousing;

a porous material having sufficient thickness and density to break up anacoustic wave and reduce the noise level of said gaseous discharge, saidporous material being mounted within said housing in substantiallyairtight contact with said solid portion so that all gaseous flow fromsaid port must pass through said porous material to reach saidperforated portion, said porous material also being spaced from one areaof said solid portion so that said gaseous flow from said port strikessaid one area without passing through said porous material;

a groove formed on said one area of said solid housing portion forcausing said solid housing portion to rupture along said groove inresponse to a predetermined pressure within said housing, said groovehaving a beginning and an end displaced a sufficient distance from saidbeginning so that the housing portions on opposite sides'of said groovewill be bent with respect to each other during said rupture, but so thatno part of said housing will be broken off and propelled from saidhousing during said rupture.

2. The noise mufi'ler of claim 1 in which: said porous materialcomprises a depth type filter which reduces said noise level to apredetermined low level and which also coalesces and removes vaporcontaminants from said gaseous flow; and

than a predetermined small obstruction to gaseous flow.

1. A noise muffler for reducing the noise level of a noise carryinggaseous discharge from a port, and having a unique safety valvecomprising: a housing having a perforated portion providing an outletpath from said housing for gaseous flow and a solid portion imperviousto gaseous flow; fitting means adapted to be attached to said port toprovide a substantially airtight path between said port and the insideof said housing; a porous material having sufficient thickness anddensity to break up an acoustic wave and reduce the noise level of saidgaseous discharge, said porous material being mounted within saidhousing in substantially airtight contact with said solid portion sothat all gaseous flow from said port must pass through said porousmaterial to reach said perforated portion, said porous material alsobeing spaced from one area of said solid portion so that said gaseousflow from said port strikes said one area without passing through saidporous material; a groove formed on said one area of said solid housingportion for causing said solid housing portion to rupture along saidgroove in response to a predetermined pressure within said housing, saidgroove having a beginning and an end displaced a sufficient distancefrom said beginning so that the housing portions on opposite sides ofsaid groove will be bent with respect to each other during said rupture,but so that no part of said housing will be broken off and propelledfrom said housing during said rupture.
 2. The noise muffler of claim 1in which: said porous material comprises a depth type filter whichreduces said noise level to a predetermined low level and which alsocoalesces and removes vapor contaminants from said gaseous flow; and themuffler includes a pleated paper filter mounted upstream from said depthtype filter to remove solid contaminants from said gaseous flow, saidremoved contaminants being held by said depth type and said pleatedpaper filters to reduce the porosity of said filters to gaseous flow Andthereby increase the pressure within said housing to ultimately causesaid rupture.
 3. The noise muffler of claim 2 in which said depth typefilter and said pleated paper filter have sufficiently largecross-sectional areas to reduce said noise level to said predeterminedlow level without providing more than a predetermined small obstructionto gaseous flow.